Refinement of the Crystal Structures of Cu<sub>6</sub>O<sub>8</sub>InCl and Cu<sub>6</sub>O<sub>8</sub>Cu<sub>2</sub>Cl by Neutron Powder Diffraction

Abstract

Two titled compounds which have different structures have been synthesized by heating mixtures of hydrates of copper (II) nitrate and copper (II) chloride, or indium nitrate. Their crystal structures have been refined by the Rietveld method using neutron powder diffraction data. Cu6O8InCl is a stoichiometric compound and has a murdochite-like structure (E. Dubler, 1983). The obtained crystallographic data are: space group Fm3m, a=9.1555 (2) A, d0=5.69g/cm3 and Z=4. Final S (=Rwp/Re) was 1.04. A [Cu6O8] block, a 3-dimensional network of 26-sided polyhedra, is composed of [CuO4] planes sharing oxygen atoms (Cu-O: 1.908A). Another block is a network of [InO8] cubes sharing corner oxygens with the 26-sided polyhedra (In-O: 2.257A). The centers of each block are occupied by Cl and In, respectively. Oxygen (32f) and chlorine sites (4b) were found to be fully occupied. This compound has been concluded to have a ordered structure with a chemical composition of Cu6O8InCl. In Cu6O8Cu2Cl, Cl sites were found to be partly substituted by NO3-. Its crystallographic data are: space group Fm3m, a=9.381 (1) A, d0=4.95g/cm3 and Z=4. S was 1.15. The crystal structure of Cu6O8Cu2Cl is essentially the same as that of Cu6O8InCl except Cu sites corresponding to the In sites. The Cu atoms are not located at the In site (2b) in the cube, but distributed among 6 equivalent sites (24e) around the center of the oxygen cube with an occupation factor of about 0.29. A Cu atom in the cube is coordinated to 4 oxygens to form a distorted [CuO4] plane with a Cu-O distance of 1.916A, and [CuO4] planes form a 3-dimensional network. Therefore, this type of compounds can be expressed as Cu6-mO8⋅Cu2-nCl0.7(NO3)0.3 where m+n are 0.4. For the sample used in this work, m was 0.1. Cu6O8Cu2Cl has a larger unit cell than Cu6O8InCl, which is explained in terms of the fact that the former contains large NO3- instead of Cl-.